This invention relates generally to well-drilling apparatus and methods and more particularly to apparatus for storing drill pipe sections in the structure of a well-drilling rig for convenient addition to and removal from the drill string.
A conventional well-drilling rig includes an upright mast with a drill table at its lower end and a rotary drive mechanism or top head drive mounted for reciprocable vertical movement at its upper end. A drill string comprising multiple sections of drill pipe is suspended from top head drive by means of a threaded drill stem. The drill string extends downwardly from the drill stem into a bore hole through a guide in the drill table. Normally, a cutter head or drill bit is mounted on the end of the drill string in the bore hole.
In operation, the top head drive turns the drill stem which turns the drill string and bit mounted thereon to bore a hole in the earth. As the drill string penetrates into the earth, additional sections of drill pipe are added to the top of the drill string. This is done by first clamping the uppermost pipe in the drill string at the level of the drill table. The drill string is next disconnected from the top drive by unthreading the drill stem from the upper end of the uppermost drill pipe. The top head is then raised to an elevated position so that another section of drill pipe can be threaded at its upper end onto the drill stem and thereafter threaded at its lower end into the upper end of the top section of drill pipe in the drill string. This process continues until a desired depth has been reached, at which time the process is reversed to remove the drill string from the bore hole.
The entire string of drill pipe must be removed from the bore hole a section at a time whenever it is necessary to change a drill bit. This procedure, known as tripping a drill string, is a repetitive, tedious and time-consuming job. The drill string is raised from the bore hole a section at a time. Before removing the uppermost pipe section from the string, the next lower drill pipe must be clamped at the drill table to support the drill string in the bore hole and prevent its rotation when the uppermost section is unscrewed. Because of the torque exerted on the drill string by the top head drive during drilling, the threads between the pipe sections frequently become jammed together. When this happens, the uppermost section of the pipe cannot be unscrewed from the drill string solely by reversing the rotary drive mechanism. The drill stem merely unscrews from the top of the uppermost pipe. Accordingly, it is necessary for workmen to break the connection between the sections by means of a large manually- or hydraulically-operated wrench. This step slows the process of tripping the drill string and is also very dangerous.
Once the uppermost pipe is loosened from the drill string, the top head drive is driven in reverse to finish unthreading it. Next, the pipe must be removed from the top head drive. This step requires immobilizing the pipe against rotation either manually or by means of a suitable clamping device, adding further complexity and time; to the process. After the pipe is removed from the drill stem, it must be stored someplace until it is to be returned to the drill string.
In the past, many efforts have been made to provide racks and magazines located on or adjacent to the drilling mast to provide a convenient storage and handling mechanism for drill pipe sections. A conventional static pipe storage rack for storing pipe sections in parallel vertical rows is shown in U.S. Pat. No. Re. 29,541 of U.S. Pat. No. 3,949,818 to Russell. Such a storage rack eliminates the need for removing the drill sections from the mast during tripping of a drill string, but still necessitates considerable handling of the pipe sections and fails to alleviate the complexity of the tripping process itself.
To ease the problems in handling drill pipe sections stored in the mast, several types of movable and rotating racks or magazines have been devised. One such device is disclosed in U.S. Pat. No. 3,025,918 to Leven. Leven provides a rotary rack device for receiving a number of drill pipe sections in a circular pattern. The device is mounted within the drilling mast for rotation about a vertical shaft parallel to the drill string. It is pivotally connected to one side of the mast for swinging lateral movement toward and away from the drill string to add pipes to and remove pipes from the string. The rack includes a bottom turntable with sockets for receiving the lower ends of four pipe sections in a single ring. An upper means rotatable support member holds the upper ends of the sections in the rack. The sockets include means for preventing turning of the pipe sections in the sockets during attachment of the drill stem. Similar devices are disclosed in U.S. Pat. Nos. 3,913,753 and 3,913,754 to Swartz, et al. and in U.S. Pat. No. 3,966,053 to Loftis.
U.S. Pat. No. Re. 30,071 of U.S. Pat. No. 3,986,569 to Hilding, et al. discloses an arcuate rack which does not rotate, but swings laterally through a semicircular arc intersecting the center line of the drill string to place pipe sections in or remove them from an arcuate slot, and to store the pipes alongside the drill string. U.S. Pat. No. 3,265,138 to Alexander, et al. discloses a similar rack having two arcuate slots arranged around a common axis of oscillation.
Although the foregoing devices reduced the pipe-handling problems inherent in the static storage rack shown in the Russell patent, their storage capacity is quite limited. Moreover, these devices still do not significantly reduce the number of steps involved in removing each section of drill pipe from the drill string. Moreover, they do nothing to solve the problem of unsticking the threads of a pipe section from those of the rest of the drill string, when such threads are jammed.
Accordingly, there remains a need for an improved method of tripping a drill string. A need also remains for improved means for storing sections of drill pipe for convenient removal from and addition to the drill string.